And depends on their age - once they hit 70, 80, 90, it can make sense to have a multi-generational household again. If you count raising your own kids as multi-generational, the times in your life where it is odd to have parents and children together are the minority. You just switch which role you play every couple decades.
More like
20 - OK
25 - hmm
28 - grow up
Ha maybe without the pandemic. But with the pandemic I would say up until 30 is completely fine... stacking mad guap
Where I'm from it's more like:
20 - Nah
25 - WTF are you serious?
30 - Hey, look at this loser over here!
Anything past university age is firm "hmm" territory in most areas.